I had one of those in a Reliant 3-wheeler. It would go up the road for 100 yards and then conk out. I'd restart the engine. Go up the road for 100 yards and the engine would conk out again. It turned out that the cone of the fuel filter had broken in half. The end was lodged in the end of the fuel pipe, restricting the flow. I removed the broken parts and all was well again.

Over a period of 15 years. I had 4 Reliant 3-wheelers. The first one fell apart faster than I could fix it. The second one, the gearbox went. The third one I sold as it was a saloon and I didn't like the 'letterbox' boot. The fourth one, the head gasket went.
15 years of amazing fun.

I had a Rialto saloon. I hated the silly 'letterbox' sized hatch for the boot. It was a right faff; Opening the hatch, then going inside to drop the rear seats so I could get my Dragunov in. At least with the Estates, I could do it all from the back. I ran Reliants for 15 years!

I've had this before and I refused to pay it.
I sold my old Reliant 3-wheeler (Don't laugh. They were great!) to somebody in Bristol. I didn't cancel the remaining insurance. The new owner insured the Reliant. A couple of weeks later, the insurance called me and asked why I hadn't canelled the remaining insurance. I told them that it was cheaper to let the remaining insurance lapse, than it was to cancel it. The insurance company blathered on about a possible claim being levelled on my insurance on the Reliant, rather than the new owners. I replied that I wasn't interested on the grounds that I didn't own the Reliant, nor was I driving it. I still wasn't going to pay the cancellation fee.
I got a refund for the remaining insurance.
You've got to play hardball with insurance companies.